The present invention relates to heavy-duty friction clutches of the type used for large automotive vehicles such as trucks, tractor-trailers, and the like and, more particularly, to a torque-limiting clutch brake assembly.
The use and function of a clutch brake are well known in the art, as discussed, for example, by Flowtow et al. (U.S. Pat. No. 4,762,215) and Babcock (U.S. Pat. No. 4,512,450). A clutch brake is a device used to facilitate shifting by retarding the rotation of transmission gears when the clutch is disengaged by the vehicle operator. Typically, a clutch brake is a disk-shaped device which is splined to the gearbox input or drive shaft of a transmission and is activated by a throw-out mechanism when the clutch is disengaged. The spinning clutch brake is thereby sandwiched between the throw-out mechanism and gearbox housing, creating a frictional drag or braking effect to slow rotation of the input shaft.
In normal use a clutch brake eventually wears out and must be replaced. This typically :requires lowering and disassembling the vehicle transmission, which is a time consuming and expensive procedure. However, Babcock (U.S. Pat. No. 4,512,450) discloses a design in which the clutch brake splits into halves so that it can be replaced without extensive disassembly of the transmission. This greatly reduces the cost of replacement.
Torque-limiting designs take a different approach. They reduce the frequency of replacement necessary by improving clutch brake longevity. They accomplish this by permitting the clutch brake to slip when excessive braking pressure is applied, thereby avoiding the excessive stresses which contribute to wear and tear. Also, unlike traditional designs, a torque-limiting clutch brake will not disrupt vehicle operation when improperly applied. Flowtow et al. (U.S. Pat. No. 4,762,215, incorporated herein by reference), for example, teaches the use of a particular friction coupling between an outer housing and inner collar member. When the torsional force between the housing and collar is too great, they slip relative to each other and thereby avoid damage.
While such torque-limiting designs work relatively well for their intended purpose, the clutch brake still eventually fails and must be replaced. However, Flowtow et al. does not teach or suggest a torque-limiting clutch brake design which splits into halves, and so it must be replaced by lowering and disassembling the clutch and transmission. Furthermore, the components used in prior art friction type torque-limiting mechanisms must be of constant dimension and have no discontinuities in order to maintain a constant slip torque. Hence, until now it has been generally thought that these designs cannot be made into splittable sections because such sections will typically have discontinuities and jam or otherwise work improperly upon use.
The present inventor's U.S. Pat. No. 5,099,970, entitled "Torque-Limiting Clutch Brake Assembly" (incorporated herein by reference) discloses a splittable, torque-limiting clutch brake which utilizes a detent mechanism as the torque-limiting feature, instead of a friction type mechanism. Use of the detent mechanism facilitates making the device in splittable halves which can be installed without removing the clutch and transmission from the vehicle.
The present invention, however, provides a friction type torque-limiting clutch brake which is also splittable into halves for easy removal and installation. It successfully overcomes the inherent difficulties in making a multi-piece friction type design in splittable halves. Moreover, the present invention uses a hinge to join one end of the two halves together in order to further facilitate installation.
Accordingly, it is a principle object of the present invention to provide an effective, long-lasting, torque-limiting clutch brake which can be removed and installed without disassembling the transmission.
More particularly, it is an object to provide a friction type torque-limiting clutch brake which can be split into halves and assembled back together.
A related object is to provide a friction type torque-limiting mechanism which is capable of being made in separable halves without jamming upon use.
A further object is to provide a torque-limiting clutch brake which can be installed with one hand through a relatively small opening.